The present invention relates to eyecups for adjustment of pupil coincidence for oculars of optical viewing instruments.
For high-precision optical instruments, so-called eyeglass oculars are used to enable a person who wears glasses to bring the pupil of his eye into the exit pupil of the ocular, so that he may thereby see the entire field of view. These eyeglass oculars are so designed that their exit pupils lie 20 to 24 mm above the ocular. In the case of normal ocular, the exit pupil is 10 to 12 mm above the ocular.
It has been the practice, in order to provide oculars which are suitable both for persons with normal eyesight and for persons who wear glasses, to provide the ocular with an eyecup of flexible material which can be rolled up. For viewing without eyeglasses, the eyecups are extended to their entire length of about 12 mm so that the exit pupil is brought into a favorable position with respect to the eyes. People who wear eyeglasses roll the eyecups down and thus have a full view of the entire field of vision with the exit pupil located a distance away. However, a standardized eyecup of the character indicated will not be of length to enable an optimal condition for users whose eye-exit pupil differs from the accepted average value, for calculation of the ocular. For brief observations, as for example through binoculars, the eye can adjust itself somewhat by adaptation to this condition. However, in jobs which require lengthy and high concentration, such as is necessary, for example, in microsurgical operations with the use of an operating microscope, the continuous need to adapt the eye is fatiguing for the observer.
Continuously axially adjustable eyecups are known from British Pat. No. 112,989; they are intended to permit adjustment for coincidence between the exit pupil of the ocular and the entrance pupil of the eye of the observer. These known adjustable eyecups consist of double-walled elastic material which can be inflated to a different height by liquid or air. The eyecups are intended to be suitable for oculars of different magnification, wherein exit pupils are at different distances above the ocular. Their disadvantage is that they are expensive to manufacture and trouble-prone in use.
British Pat. No. 313,126 discloses rigid eyecups for binocular telescopes wherein the eyecups are continuously axially adjustable jointly, via an arm which is fastened to central focusing means. For modern purposes, this displacement mechanism is too expensive and too bulky in construction.